Circuit for driving the pulse motor

ABSTRACT

The circuit for driving the pulse motor applies a high voltage to the exciting coil of the pulse motor when the rotor of the pulse motor rotates. The current of the exciting coil is detected in the detector circuit, and when said current reaches a predetermined valve, said high voltage applied to the exciting coil changes to a low voltage. That is, the circuit of the application is composed of a high voltage source, a low voltage source, a detector circuit, and circuit for changing from said high voltage source to said low voltage source.

United States Patent 11 1 Inaba et al.

CIRCUIT FOR DRIVING THE PULSE MOTOR Inventors: Seiuemon lnaba; KanryoShimizu, both of Kawasaki; Toshio Kojima, Yamato, all of Japan FujitsuLimited, Kanagawa-ken, Japan Filed: July 1, 1971 Appl. No.: 158,831

Assignee:

Foreign Application Priority Data July 6, 1970 Japan 45/58877 US. Cl318/696, 318/440, 318/685, 318/434 Int. Cl. H02k 37/00 Field of Search318/696, 685, 254, 318/138, 432, 434, 440

References Cited UNITED STATES PATENTS 2/1971 Beling 318/138 F 60 INV e[4 1 Sept. 4, 1973 3,452,263 6/1969 Newell 318/696 3,355,646 11/1967Goto..... 318/138 3,424,961 l/1969 Leenhouts 318/696 Primary ExaminerG.R. Simmons Attorney-Nelson E. Kimmelman et a1.

[57] ABSTRACT The circuit for driving the pulse motor applies a highvoltage to the exciting coil of the pulse motor when the rotor of thepulse motor rotates. The current of the exciting coil is detected in thedetector circuit, and when said current reaches a predetermined valve,said high voltage applied to the exciting coil changes to a low voltage.That is, the circuit of the application is composed of a high voltagesource, a low voltage source, a detector circuit, and circuit forchanging from said high voltage source to said lowvoltage source.

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PATENTEB SEP 4mm sum 2 0r 4 INV3 F3 CIRCUIT FOR DRIVING 'II'IE PULSEMOTOR The present invention relates to a circuit for driving a pulsemotor, and especially relates to a circuit which applies a high voltageto a pulse motor when the rotor revolves, and applies a low voltage tothe pulse motor when the rotor is in its stopped condition.

Generally, the pulse motor repeates the movement and the stop by controlfrom the input control signal, then rotates to the predetermined anglein a step manner. Now, the mechanical work of the pulse motor, that isthe power, is used only when the rotor of the pulse motor is actuallymoving. Accordingly, it is preferable that the high voltage of the inputelectric power is supplied only when the rotor is moving, and a lowvoltage is supplied when the rotor is stopped.

The conventional method which realizes this purpose uses a seriesresistor to change the value of the current flowing in the exciting coilof the pulse motor. However, this method has the defect that theelectric power loss in the series resistor is considerable and thus highefficiency can not be expected. Another method exchanges the highvoltage source with the low voltage source in a predetermined fixedperiod. However, the circuit realizing this method is very complex,because the current flow in the exciting coil increases exponentially sothat the setting of the commutation time in a high speed operation isvery difficult.

The object of the present invention is to overcome the above-mentioneddrawbacks.

A further object of the present invention is to provide a circuit whichdetects an exciting current in the exciting coil and when said excitingcurrent reaches a predetermined value, the voltage source is changedfrom high to low.

A still further object of the present invention is to provide a circuithaving excellent efficiency and reliability.

Further features and advantages of the present invention will beapparent from the ensuing description with reference to the accompanyingdrawings to which, however, the scope of the invention is in no waylimited.

FIGS. 1A to 1C are diagrams and waveforms explaining the function of thepulse motor,

FIGS. 2A and 2B are respectively block diagram and waveforms of oneembodiment of the present invention,

FIGS. 3A and 3B are schematic driving circuits relating to one phase ofthe pulse motor, and

FIG. 4 is a diagram showing the waveforms at the essential points ofFIG. 3.

Referring to FIG. 1A, the pulse motor repeats a step and a stop underthe control of the input control signal and revolves through apredetermined angle in a step manner. Thus the mechanical work, that isthe output of the pulse motor, is produced pulsatingly as shown in FIG.18. Accordingly, the efficiency of the pulse motor can be considerablyincreased by providing the input electric power in an impulse manner asshown in FIG. 1C. That is, the current i, is drawn during the periodthat the rotor is stopped and the current i, is drawn during the periodthat the rotor rotates from one magnetic stable point to anothermagnetic stable point, and does work.

FIG. 2A is one example of the embodiment of the driving circuit of afive-phase pulse motor EPM. The

exciting coils l 5 of each phase are connected respectively to twotransistors actuated as switching elements. One of said transistors isconnected to the high voltage source V, and is provided as the highvoltage switch. The other of said transistors is connected to the lowvoltage source V, via the exciting coil and a diode. The detectingcircuits DCl to DCS detect the exciting current in the exciting coils,and when the exciting currents reach a predetermined value, theflip-flops F1 to F5 reset and the high voltage switch transistors 0,, Q0,, Q, and Q cut-off and the low voltage source V, is applied to theexciting coils.

Referring to FIG. 2A, the command pulse CP as shown in FIG. 2B isapplied to a positive direction terminal CW or a negative directionterminal CCW of the two phase-three phase alternative exciting controlcircuit SR. The exciting control circuit SR then distributes the controlsignals from its output terminals (a e) as shown in FIG. 28 so as torepeat alternatively the two phase excitation and the three phaseexcitation in the predetermined phase order. These control signals aresupplied to the driving circuit of the pulse motor.

FIG. 3A shows a driving circuit diagram of one phase of a poly-phaseelectric pulse motor. Referring to FIG. 3A, a coil EPM of an electricpulse motor is connected via a transistors Q, and Q, and a resistor r toa high voltage electric source V,, and a low voltage electric source V,is connected via a diode D, to a connection point between the emitter ofthe transistor Q, and the coil EPM of the electric motor, and aconnection point between the coil EPM and the collector of thetransistor Q, is connected via a diode D, and a resistor R, to the highvoltage potential. The input terminal IN is connected to an inverterINV, the output of the inverter is connected to a set terminal of aflip-flop circuit F, and the output of the flipflop circuit F isconnected via an amplifier A, to the base of the transistor 0,. Also,the input terminal IN is connected via an amplifier A, to the base ofthe transistor 0,. This constitutes the changing circuit. The seriescircuit consisting of a Zener diode ZD and a variable resistor VR isconnected to both terminals of the resistor r, and the connection pointbetween the Zener diode ZD and the variable resistor VR is connected viaa mono-stable cir cuit MM to the reset terminal of the flip-flop circuitF. As mentioned above, this constitutes the detecting circuit of theexciting current.

On the one hand, when an input signal e, as shown in (a) of FIG. 4 isapplied to the input terminal IN, said signal e is supplied to the baseof the transistor Q, and said transistor Q, is made to conduct. On theother hand, said input signal e is inverted by the inverter INV, and theinverted signal e, as shown in (b) of FIG. 4 is applied to the setterminal of the flip-flop F. The falling time in the leading edge of thesignal e, sets the flip-flop F and an output e, of the flip-flop F asshown (g) of FIG. 4 is supplied via the amplifier A, to the base of thetransistor Q1, and the transistor Q, conducts. As a result of this, thecurrent I as shown in (e) of FIG. 4 flows from the high voltage sourceV, through exciting coil EPM. This current I increases exponentially dueto the inductance of the exciting coil EPM, as shown in (e) of FIG. 4.The increase in value of the current I is detected as the voltage dropacross the resistor r. The variable resistor VR is adjusted so that thecurrent detected by the resistor r rises above the voltage of the Zenerdiode ZD and is applied to the mono-stable multivibrator MM when saidcurrent reaches the predetermined value. Then the voltage e of themono-stable multivibrator MM shown (I) in FIG. 3 which exceeds thevoltage of the Zener diode ZD is applied to the reset terminal of theflip-flop F, and the falling edge of the signal e puts the flip-flop Finto the reset state so that the output pulses e, of the flip-flop Ffall to zero as shown in (g) of FIG. 4. Accordingly, the transistor Q iscut-off. However, the transistor Q is maintained in the on state, andthe current flows from the low voltage source V through exciting coilEPM via the diode D,. Then the current I decreases as shown in (e) ofFIG. 4. Another embodiment of the detecting circuit is shown in FIG. 3B.In this circuit, an input trigger level of the mono-stable multivibratorMM is fixed at a predetermined level by the variable resistor VR, aresistor R, and a bias voltage V. When the voltage drop in the resistorr exceeds said predetermined level, said voltage is applied viaresistors R R and a capacitor C to the monostable multivibrator MM. Andthe output e of the mono-stable multivibrator MM shown in (f) of FIG. 4is applied to the reset terminal of the flip-flop circuit F. A counterelectromotive force is produced in the exciting coil by said suddendecrease of the current I, and, said force is fed back to the highvoltage source V via the diode D and the resistor R,. Next, the inputsignal e falls to zero, and the transistors are both cutoff, and thecurrent passing through the exciting coil EPM falls to zero.

The conduction time t, of the transistor Q which is connected betweenthe exciting coil EPM and the high voltage potential V, is selectivelydetermined by the values of the resistor r, the voltage of the Zenerdiode ZD and the variable resistor VR. However, said conduction time t,must be determined taking into consideration the moment of inertia ofthe pulse motor which includes the mechanical load, and self inductanceof the exciting coil. Further, the variable resistor VR is provided foradjusting precisely the said conduction time t,.

As mentioned above, according to the driving circuit for the electricpulse motor of the present invention, a rapid rise edge of the excitingcurrent and a rapid response time can be expected, and the electricpower loss can be reduced by controlling the exciting current to itspredetermined value. Further, the transistors used for the switchingelements will not deteriorate due to excessive current, because even inthe case where a layer short-circuit occurs in the exciting coils of thepulse motor, the detecting circuit detects the current and commutates tothe low voltage source. Further, the current supplied by the highvoltage source is maintained constant, then the torque is maintained inconstant both at low and high speeds.

It is understood that other current detecting means, such as, forexample the hole effect, can be utilized as the current detectingcircuit, and the switching element and the gate circuit except for thetransistors can be utilized as the commutating circuit.

What is claimed is:

1. A circuit for driving a multiphase pulse motor in response to acontrol signal from a generator therefor comprising for each phase ofsaid motor:

an exciting coil,

means including a first switching element for coupling with a firstterminal of said coil to a high voltage source,

means for coupling said first terminal to a low voltage source, secondswitching element coupled between a second terminal of said coil and areference potential, signal path coupled between said generator and saidfirst switch element which includes means for controlling said firstswitching element, changing circuit coupled between said generator andsaid second switching element for controlling said second switchingelement, and detector circuit coupled between said means for controllingsaid first switching element and said second switching element,

said signal path and said changing circuit initially causing said firstand second switching elements to be conductive in response to thebeginning of said control signal, whereupon an exciting current flowssolely from said high voltage source through said coil, therebydecoupling said low voltage source from said first terminal thereof,until it reaches a predetermined value at which said detector circuitcauses said controlling means in said signal path to cut off said firstswitching element, which thereby cuts off the current from said highvoltage source whereupon said coil is traversed solely by current fromsaid low voltage source until the end of said control signal at whichtime said second switching element is cut off and said low voltagecurrent no longer flows through said coil.

2. The circuit accordingto claim 1 wherein said first and secondswitching elements are solid-state transistors whose collectors andemitters are in series with said coil.

3. The circuit according to claim I wherein said signal path includesmeans responsive to said control signal for producing a pulse having aduration shorter than the duration of said control signal thereby torender said first switching element conductive for a time shorter thansaid second switching element.

4. The circuitaccording to claim 1 wherein said detector circuitincludes voltage-level sensing means and a monostable multivibrator forproducing a sharp pulse which, when applied to said signal path causesthe controlling means therein to terminate the signal produced thereinwhich renders said first switching element conductive.

1. A circuit for driving a multiphase pulse motor in response to acontrol signal from a generator therefor comprising for each pHase ofsaid motor: an exciting coil, means including a first switching elementfor coupling with a first terminal of said coil to a high voltagesource, means for coupling said first terminal to a low voltage source,a second switching element coupled between a second terminal of saidcoil and a reference potential, a signal path coupled between saidgenerator and said first switch element which includes means forcontrolling said first switching element, a changing circuit coupledbetween said generator and said second switching element for controllingsaid second switching element, and a detector circuit coupled betweensaid means for controlling said first switching element and said secondswitching element, said signal path and said changing circuit initiallycausing said first and second switching elements to be conductive inresponse to the beginning of said control signal, whereupon an excitingcurrent flows solely from said high voltage source through said coil,thereby decoupling said low voltage source from said first terminalthereof, until it reaches a predetermined value at which said detectorcircuit causes said controlling means in said signal path to cut offsaid first switching element, which thereby cuts off the current fromsaid high voltage source whereupon said coil is traversed solely bycurrent from said low voltage source until the end of said controlsignal at which time said second switching element is cut off and saidlow voltage current no longer flows through said coil.
 2. The circuitaccording to claim 1 wherein said first and second switching elementsare solid-state transistors whose collectors and emitters are in serieswith said coil.
 3. The circuit according to claim 1 wherein said signalpath includes means responsive to said control signal for producing apulse having a duration shorter than the duration of said control signalthereby to render said first switching element conductive for a timeshorter than said second switching element.
 4. The circuit according toclaim 1 wherein said detector circuit includes voltage-level sensingmeans and a monostable multivibrator for producing a sharp pulse which,when applied to said signal path causes the controlling means therein toterminate the signal produced therein which renders said first switchingelement conductive.